The problem with cyano-B12 is that it can only be absorbed in the gut, which reduces the absorption rate to 1 %. Hydroxo and methyl-B12 can be absorbed sublingually which gives it an absorption rate of approximately 20 %. It is, in other words, difficult to get enough cyano-B12 into your body without injecting it intravenously.
Iron can make a large difference for your well-being, but beware - if the effects are immediate (within an hour or two) it may have to do with the effects of free radicals (breaking down the instable enzyme methionine synthase, re-routing methylfolate towards BH4 production and thereby increasing dopamine) rather than increasing iron stores in the body.
I'm curious though - have you noticed any observable signs or other symtoms in addition to your cognitive symptoms, like skin changes, infections, itching or such? It would be interesting to see a summary of all the symptoms you are experiencing
As to my symptoms, I have a diagnosis of ADHD-PI, though the emerging concept of Sluggish Cognitive Tempo (SCT) is probably more applicable. It is nothing recent--I've had lifelong issues with attention, focus, working memory, mental fatigue, sluggish processing, malaise, amotivation, asociality, etc. It runs in my family, too, so seems as genuine a case of ADHD-PI/SCT as you could find.
I am now interested in the idea that I may have had life-long low or borderline low iron, maybe a genetic predisposition to such, though I'm not going to assume anything. In some ways it would make sense: I've always had extra pale skin, fatigue easily, out of breath easily, etc. I remember distinctly having a lot less stamina than my friends as a child. In more recent years I have also noticed a tendency to bruise, and there are times when physical activity causes me to feel dizzy or generally unwell. These things seem in line with some of the iron deficiency symptoms I've read about. And, there are at least a couple of studies showing a strong association between ADHD and low iron status.
When I began iron supplementation, the effects were quite rapid. I feel more energetic, less fatigued, though time will tell on that. Also, my coloring appears affected. My hands for example seem to have a deeper and more reddish hue than normal.
I'm skeptical, and am prepared to be disappointed. It wouldn't be the first time. However, it is an interesting turn of events, worth exploring.
Your comment about the potential effect of free radicals is interesting. What are the signs that this would be the case? Is it at least feasible that my life-long issues could be related, at least in part, to iron status?